It is already known from DE-A 4 332 738 that optically active, primary and secondary amines can be prepared by initially enantioselectively acylating racemic amine in the presence of a hydrolase using an ester which has an electron-rich heteroatom in the acid moiety in the vicinity of the carbonyl carbon atom, then separating the resulting mixture of optically active (S)-amine and optically active acylated (R)-amine (=amide), thereby affording the (S)-amine, and obtaining the other enantiomer, if desired, from the acylated (R)-amine by amide cleavage. Suitable hydrolases are lipases from Pseudomonas, for example Amano P, or from Pseudomonas spec. DSM 8246. The degree of optical purity of the enantiomers that are obtained is very high. However, this process has the disadvantages that relatively long reaction times are required for the enzymatic acylation and that the reaction is carried out in highly dilute solution. Only after relatively long reaction times is the remaining (S)-enantiomer obtained in sufficiently high optical yield. For practical purposes, the space-time yields that can be achieved are therefore inadequate. It is a further disadvantage that relatively high amounts of enzyme are required with respect to the substrate. Besides, the enzyme has very high activity, so that purification, concentration and work-up requires considerable effort. Moreover, a relatively expensive acylation component is necessary.
Furthermore, Chimica 48, 570 (1994) discloses that racemic amines will react enantioselectively with ethyl acetate in the presence of lipase from Candida antarctica to give mixtures of (S)-amine and acetylated (R)-amine (=amide) from which (S)-amine and acetylated (R)-amine can be isolated, it being possible to set free the acetylated (R)-amine by subsequent amide cleavage. Disadvantages of this method are that once more relatively long reaction times are required and that furthermore the yields are not always satisfactory. In addition, the ratio of enzyme to substrate is again so disadvantageous that an economical utilization of the process is scarcely possible.